Conventionally, there is known a method of etching a silicon nitride (SiNx (x is a natural number), SiCN, SiON, etc.) by using plasma.
A conventional plasma etching method is described in, for example, Patent Document 1. In this plasma etching method, a processing target object having a silicon nitride layer and a first mask formed on the silicon nitride layer is prepared, and the processing target object is placed and etched in a plasma processing apparatus. The plasma etching method includes a first process of supplying a processing gas containing oxygen (O2) and fluorocarbon (CHxFy) (x and y are appropriate integers), and a second process of etching the silicon nitride layer of the processing target object with the first mask by exciting the processing gas into plasma.
Patent Document 1: Japanese Patent No. 3,681,533
When an etching temperature is high, however, a diameter of a hole formed by etching the silicon nitride layer is decreased toward a deep portion thereof, so that the hole finally has a shape in which a tip end portion thereof becomes narrowed (i.e., tapered shaped). Meanwhile, when the etching temperature is low, the diameter of the hole becomes much larger than an opening diameter of the mask which is originally designed. That is, a hole without having the tapered shape and the larger diameter cannot be formed in the silicon nitride, neither when the temperature is high nor when the temperature is low.